Gravel Sea Cucumber

This issue's species of the month is the gravel sea cucumber which is found in coarse gravel or mearl. It can grow to about 20 cm long and lives in the substratum with only its tentacles visible when extended. It can quickly pull them in if threatened. Its body has numerous calcareous deposits on the skin and tapers towards either end. Around the mouth there are profusely branching tentacles. The cucumber mops the surface on which it is feeding with its mucus-covered tentacles before drawing them back, one at a time, into the mouth to be sucked clean of any particles.

The gravel sea cucumber can move along the seabed by using its 'tube feet' which are fluid-filled muscular tubes with suckers. It can also make its body soft or hard. If this sea creature wants to squeeze through narrow cracks, it can make its body soft and very flexible and if it wants to bury its body in the seabed, it can make its body hard and stiff. They do this by using a compound in their skin called catch collagen - this tissue is under neurological control and is capable of changing from a 'liquid' to a 'solid' form very quickly.

When a sea cucumber is really threatened it can respond by ingesting a volume of water and physically rupturing (literally exploding) the hind gut to expel these tubules and a soup of defensive chemicals that are intended to prevent the predator from ever wanting to prey on a sea cucumber again.

Latin name: Neopentadactyla mixtaHabitat: The gravel sea cucumber lives within coarse, typically mobile shell, sand, gravel or maerl where tidal flow is quite strong.Distribution: They are found all up the west coast of Scotland to Orkney and Shetland. A few isolated records from the east coast. Also from SW England, SW and NW Wales. In Ireland, particularly in Kilkieran Bay.Size: 20cm Tentacles: 20 tentacles; 10 large, 5 intermediate and 5 small. Reference: www.advancedaquarist.com/2003/1/inverts